Скачать или смотреть Geometric Series (Q15 A2 P2 Edexcel 2022)

In this video, Lee Guffick breaks down a challenging A Level Maths geometric series question from the Edexcel A2 2022 Paper 2.
Lee shows how to use the common ratio method to derive a trigonometric quadratic, solve it under the condition that theta is obtuse, and then calculate the sum to infinity of the geometric series. This is an excellent example of an A grade and A star reasoning question requiring algebraic manipulation, trigonometric identities, and precise problem-solving.

Whether you're aiming for top grades or revising the hardest topics on the A Level syllabus, this walkthrough will help you understand exactly how examiners expect you to structure your reasoning.

⏱️ TIMESTAMPS:
00:00 Introduction
00:02 Using u2 divided by u1 and u3 divided by u2 to form the common ratio
01:15 Expanding and rearranging to derive the quadratic
02:40 Solving using factoring when theta is obtuse
04:50 Interpreting sin theta equals one half on the unit circle
05:20 Finding theta equals five pi over six
06:00 Identifying a and r for the geometric series
07:00 Calculating the sum to infinity and rationalising
09:00 Final answer and exam tips

✏️ TOPICS COVERED:

Geometric series and common ratio

Forming and solving trigonometric quadratics

Factoring using the rainbow split method

Using obtuse angle conditions to select correct solutions

Finding a and r and calculating S infinity

Rationalising surd expressions

💯 EXAM TIPS:

When dealing with geometric series, u2 divided by u1 equals u3 divided by u2 is nearly always the fastest route.

If an angle is stated as obtuse, immediately restrict your solutions to the second quadrant.

Always check whether your trigonometric solutions fall within the domain of the question.

For S infinity, remember the formula works only when the modulus of r is less than one.

State exact values wherever possible – examiners love precision.

📚 ABOUT GUFFICK TUITION:
Lee Guffick is a former Head of Mathematics and A Level Examiner, helping students secure A star and A grades and win places at Oxford, Cambridge, and the Ivy League. His expert walkthroughs are designed to build intuition, confidence, and exam technique.

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